1. Field of the Invention
The present invention relates to a fuel cell and a fuel cell system capable of increasing the efficiency of electric power generation.
2. Description of the Related Art
A fuel cell generates electric energy by electrochemical reaction of combining a hydrogen and oxygen. Such a fuel cell has generally a laminated structure in which a plurality of unit fuel cells is laminated as a FC stack.
Each unit fuel cell comprises an electrode membrane, an air electrode, and a fuel electrode. The electrode membrane is placed between the air electrode (as a cathode electrode) and the fuel electrode. The air electrode and the fuel electrode are hold by separators through which an oxidant gas (as cathode gas) and a fuel gas are introduced and flow. Air is used as the oxidant gas and hydrogen gas is used as the fuel gas.
The magnitude of the output electric power from the fuel cell is determined by the concentration of oxygen involved in air to be supplied to the fuel cell. Accordingly, the increasing of the output electric power of the fuel cell needs to increase the oxygen concentration in the air to be supplied to the fuel cell.
There are plural conventional techniques that have disclosed how to increase the oxygen concentration in air to be supplied to a fuel cell. Japanese patent laid open publications 2003-229165 and H10-321249 have disclosed a means to generate pure oxygen and to add the generated oxygen to air to be supplied to a fuel cell. A Japanese patent laid open publication 2003-217624 has disclosed a method how to increase the amount of air to be supplied to a fuel cell.
However, those conventional techniques involve drawbacks, for example, the former techniques disclosed by the Japanese patent laid open publications 2003-229165 and H10-321249 need the means with a complicated configuration and require to keep a place where the means is installed. The latter technique disclosed by the Japanese patent laid open publication 2003-217624 causes increasing of the power consumption of the means such as a compressor in order to increase the amount of the air supply. This technique also decreases the entire efficiency of the fuel cell system.
In general, the oxygen concentration in the air flowing through an air channel in the fuel cell takes the lowest value at the place near an air outlet in the air channel. This means that the oxygen in the air is consumed by the electric generation during the air flow from an inlet to the outlet of the air channel, and the oxygen concentration is thereby gradually decreased and, on the other hand, the amount of water vapor in the air is gradually increased because the water generated in the electric generation becomes water vapor and added into the air.
Accordingly, it may be considered that the increasing of the output power of the fuel cell requires increasing the oxygen concentration in the air at the area near the air outlet of an air channel.